Biodegradable resin compositions and laminates based thereon

ABSTRACT

A biodegradable resin composition including a saponified ethylene-vinyl acetate copolymer and a starch-based macromolecular substance. The saponified ethylene-vinyl acetate copolymer is one having an ethylene content of 20 to 60 mole %, a vinyl acetate saponification degree of not less than 90 mole %, a melt flow index of 1 to 100 g/10 min as measured under a load of 2160 g at 210° C., and a melt viscosity ratio η 60  /η 5  of 0.5 to 4 where η 60  means the melt viscosity after 60 minutes of standing at 250° C. and the η 5  means the melt viscosity after 5 minutes of standing at 250° C. and a starch-based macromolecular substance. A layer of the above composition can be used to fabricate a laminate with a substrate material of a different kind, such as a photodegradable polymer.

TECHNICAL FIELD

The present invention relates to a biodegradable resin compositioncomprising a saponified ethylenevinyl acetate copolymer and astarch-based macromolecular substance and to a laminate utilizing thesame.

BACKGROUND ART Prior art

Molded plastic products such as plastic packaging films and containers,agricultural plastic films, binding tapes and so on are sometimesdisposed of in ways other than legitimate routes of disposal. Becausethese products retain their shapes for years, they present seriousenvironmental problems when discarded as they are. Therefore, it ishighly desirable that any shaped products that are liable to bediscarded in the open field, farmlands, rivers, etc. be those which willbe rapidly decomposed by microorganisms in the soil or water.

Against this background, much development work has been undertaken todevelop biodegradable compositions for the fabrication of suchbiodegradable shaped products. Referring to research and developmentalong this line, the following patent applications have been filed inthe technical field of bio-degradable or disintegratable compositionseach comprising a saponified ethylene-vinyl acetate copolymer (i.e.ethylenevinyl alcohol copolymer) and a starch-based macromolecularsubstance.

Japanese Patent Kokai Publication No. 3-31333

The official gazette of Japanese Patent Kokai Publication No. 3-31333discloses a polymer composition for the manufacture of shapedbiodegradable plastic products which comprises an ethylene-vinyl alcoholcopolymer and a modified starch wherein the ethylene content of saidethylene-vinyl alcohol copolymer is 10 to 90 weight % and the melt flowindex thereof is 2 to 50. The melt flow index here is the valuedetermined at 230° C. under a load of 2.16 kg. The same gazette statesthat the preferred parameters of the ethylenevinyl alcohol copolymer areas follows.

Intrinsic viscosity [η] (in dimethyl sulfoxide, 30° C.): 0.5-0.9,preferably 0.60-0.80

Molecular weight distribution Mw/Mn (GPC in tetrahydrofuran): 1.3-4

Melting point: <180° C., preferably 160°-170° C.

Degree of hydrolysis: 90-99.9%

The same gazette states that, as the plasticizer, a polyol such aspolyethylene glycol having a molecular weight of 200 to 4000, ethyleneglycol, propylene glycol, sorbitol, or preferably glycerin can beemployed.

Japanese Patent Kokai Publication No. 2-14228

The official gazette of Japanese Patent Kokai Publication No. 2-14228discloses a polymer blend obtainable from a melt comprising awater-containing starch hydrolyzate and at least one substantiallywater-insoluble synthetic thermoplastic polymer. Claim 4 in the Scope ofDemand for Patent of this gazette is directed to the use, as thethermoplastic polymer, of ethylene-vinyl acetate copolymer,ethylene-vinyl alcohol copolymer, ethylene-acrylic acid copolymer,ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer,ABS copolymer, styrene-acrylonitrile copolymer or polyacetal, thusreferring to ethylene-vinyl alcohol copolymer, but there is nodescription about its ethylene content, nor does the specificationinclude an example employing an ethylene-vinyl alcohol copolymer.

This gazette mentions, as the plasticizer, a variety of plasticizerssuch as low molecular weight polyalkylene oxides, e.g. polyethyleneglycol, polypropylene glycol, polyethylenepropylene glycol, etc., lowmolecular weight organic plasticizers such as glycerol, glycerolmonoacetate, diacetate or triacetate, etc., as well as propylene glycol,sorbitol, sodium diethylsulfosuccinate, triethyl citrate, tributylcitrate and so on.

Japanese Patent Kokai Publication No. 3-24101

The official gazette of Japanese Patent Kokai Publication No. 3-24101discloses a method of producing a modified starch composition for themanufacture of shaped biodegradable plastic products which comprisesblending starch with a high boiling plasticizer and a modifying agentselected from among urea, alkaline earth or alkali metal hydroxides andmixtures thereof at a temperature of 120° to 170° C. which is lower thanthe boiling point of the plasticizer for a sufficient time to modify thestarch. Claim 5 in the Scope of Demand for Patent of this gazette statesthat the blending is performed in the presence of up to 15 weight % ofthe total weight of the mixture of an ethylene-acrylic acid copolymerand/or a polyvinyl alcohol. Furthermore, immediately preceding theExamples, the same gazette states that this modified starch compositionis suited for blending with an ethylene-vinyl alcohol copolymer and anexample is given as Example 5 in which a composition comprising 60weight % of modified starch in the pellet form and 40 weight % of anethylene-vinyl alcohol copolymer (Kuralene R20 (trademark)) is extruded.However, there is no specific reference to the ethylene content.

This gazette mentions, as the preferred plasticizer, such species asglycerin, polyethylene glycol, preferably polyethylene glycol having amolecular weight of 200 to 4000, ethylene glycol, propylene glycol,sorbitol and so on.

Problems that the Invention is to Solve

Any biodegradable/disintegratable composition comprising anethylene-vinyl alcohol copolymer and a starch-based macromolecularsubstance contains a large amount of the starch-based macromolecularsubstance which is liable to undergo pyrolysis in melt-molding and theethylene-vinyl alcohol copolymer contained is also one of the resinscomparatively difficult to melt-mold among the ordinary thermoplasticresins. Therefore, in this binary system, molding troubles such asdeposits of burned resin around the die, gelation, coloration on aging,fish eye, etc. tend to take place in long-run production. In order tosupply a biodegradable/disintegratable product at low cost and on asteady basis in such a binary system, these problems associated withlong-run moldability must be overcome.

However, in the gazette of Japanese Patent Kokai Publication No. 3-31333referred to above, the ethylene-vinyl alcohol copolymer is selected onlywith reference to the commonplace indicators such as ethylene content,degree of saponification, melt flow index, intrinsic viscosity (anindicator of molecular weight), melting point and molecular weightdistribution and, in regard to the melt characteristics of resin,attention is paid only to the parameters of melting point and melt flowindex. Check experiments of the Examples described in Japanese PatentKokai Publication No. 3-31333 indicate that although early moldabilityis acceptable on the whole, a variety of defects develop in moldings onlong-run molding. This is probably because they did not have a definiteidea about the melt characteristics necessary for long-run molding.

The official gazette of Japanese Patent Kokai Publication No. 2-14228shows no specific example in which an ethylene-vinyl alcohol copolymermight have been actually used and, of course, the long-run moldabilitywith this copolymer is not discussed.

Example 5 in the official gazette of Japanese Patent Kokai PublicationNo. 3-24101 indicates an example in which a composition comprising 60weight % of pelletized modified starch and 40 weight % of anethylene-vinyl alcohol copolymer was extruded using an extruder butthere is no discussion on the melt characteristics of the copolymer, noris the subject of long-run moldability explored, irrespective of the useof the copolymer.

After all, the above official gazettes of Japanese Patent KokaiPublication Nos. 3-31333, 2-14228 and 3-24101 show a mere backgroundtechnology concerning the biodegradable/disintegratable compositioncomprising a saponified ethylene-vinyl acetate copolymer (ethylene-vinylalcohol copolymer) and a starch-based macromolecular substance and thelong-run moldability of such a binary system remains to be elucidatedyet.

Moreover, as mentioned above, any starch-based macromolecular substanceis thermolabile and, when it is blended with a resin and subjected tomelt-forming, undergoes pyrolysis at temperatures above about 180° C. Onthe other hand, the saponified ethylene-vinyl acetate copolymer is oneof the thermoplastic resins which are difficult to melt-form. Forexample, the melting point of a highly saponified ethylene-vinyl acetatecopolymer is not less than 180° C. when its ethylene content is about 30mole % or less. Therefore, a binary system comprising these twomaterials tends to cause molding troubles or defects in shaped products.Therefore, in commercial production, it is essential to incorporate avariety of plasticizers mentioned above prior to molding. However, theapplication of those plasticizers which are commonly used in theconventional processes to the binary system comprising a saponifiedethylene-vinyl acetate copolymer and a starch-based macromolecularsubstance results in the problem of poor compatibility, inadequacy inthe clarity and flexibility of the film or sheet formed therefrom, andchanges in physical properties and contamination owing to bleeding ofthe plasticizer. Thus, improvements that would satisfy all of theserequirements have been much awaited.

It is an object of the present invention to provide a resin compositioncapable of providing a biodegradable or biodisintegratable shapedproduct.

It is a further object of the invention to improve the melt-moldability,particularly long-run moldability, of a binary system comprising asaponified ethylene-vinyl acetate copolymer and a starch-basedmacromolecular substance.

A further object of the invention is to provide a resin compositionwhich, when molded into film or sheet with the aid of a plasticizer,insures satisfactory clarity and flexibility and is less liable toundergo changes in physical properties or fouling due to bleeding of theplasticizer.

A still further object of the invention is to provide said compositionconducive to a reduced amount of the plasticizer required.

It is a further object of the invention to provide a laminate comprisinga layer composed of said composition and a backing layer (particularly asubstrate film composed of a photodegradable polymer).

DISCLOSURE OF INVENTION

The biodegradable resin composition of the present invention comprises asaponified ethylene-vinyl acetate copolymer having an ethylene contentof 20 to 60 mole a vinyl acetate saponification degree of not less than90 mole %, a melt flow index of 1-100 g/10 min. as measured under a loadof 2160 g at 210° C. and a melt viscosity ratio η₆₀ /η₅, between themelt viscosity η₆₀ after 60 minutes at 250° C. and the melt viscosity η₅after 5 minutes at 250° C., of 0.5-4 and a starch-based macromolecularsubstance.

The laminate of the present invention is a laminar structure comprisinga layer comprosed of said biodegradable resin composition and a layercomposed of a different material (particularly at least onephotodegradable polymer selected from the group consisting ofethylene-CO copolymer, ethylene-vinyl ketone copolymer, polybutadieneand isoprene rubber or a polyolefin type photodegradable polymercontaining at least one of said polymers).

The present invention is now described in detail.

Saponified ethylene-vinyl acetate copolymer

As the saponified ethylene-vinyl acetate copolymer, a copolymer havingan ethylene content of 20-60 mole %, preferably 25-50 mole %, and avinyl acetate saponification degree of not less than 90 mole %,preferably not less than 95 mole % is employed. If the ethylene contentis less than 20 mole %, the melt-moldability of the composition issacrificed. If 60 mole % is exceeded, the mechanical strength and gasbarrier property of the product are impaired so that the practicalutility of the composition is compromised. If the vinyl acetatesaponification degree is less than 90 mole %, the mechanical strengthwill not be sufficient. Moreover, outside of the above-mentioned range,not only the physical characteristics of the product but also thecompatibility of the polymer with the starch-based macromolecularsubstance is adversely affected.

As the saponified ethylene-vinyl acetate copolymer, two or more speciesvarying in ethylene content can be employed in combination. An exampleis the use, in combination, of a saponified ethylene-vinyl acetatecopolymer having an ethylene content of 40-60 mole % and a saponifiedethylene-vinyl acetate copolymer having an ethylene content of 20-50mole %, the ethylene content of the former being greater than that ofthe latter by at least 5 mole %, in a weight ratio of 70:30 through30:70.

Within the limits not jeopardizing the object of the invention, thesaponified ethylene-vinyl acetate copolymer of the above composition mayhave been modified by copolymerization with other copolymerizablemonomers [other α-olefins, ethylenically unsaturated carboxylic acidcompounds (acids, anhydrides, salts, esters, amides, nitriles, etc.),vinyl ethers, vinyl esters other than vinyl acetate, ethylenicallyunsaturated sulfonic acid compounds (acids, salts, etc.),oxyalkylene-containing monomers and so on] or "postmodified" byoxyalkylene-etherization, cyanoethylation, acetalization, urethanation,etc.

Regarding the melt-characteristics of the saponified ethylene-vinylacetate copolymer having the above composition, it is first of allnecessary that the copolymer should have a melt flow index of 1 to 100g/10 min, preferably 1 to 60 g/min, and more preferably 2 to 30 g/10min, as measured under a load of 2160 g at 210° C. If the melt flowindex is outside of the above range, the polymer will be unqualified asa melt-molding grade.

Another essential melt-characteristic for the saponified ethylene-vinylacetate copolymer for use in accordance with the invention is that themelt viscosity ratio η₆₀ /η₅, i.e. the ratio of the melt viscosity η₆₀after 60 minutes at 250° C. to the melt viscosity η₅ after 5 minutes at250° C., should be 0.5 to 4 and preferably 0.8 to 2.5. This is anessential element of the present invention. If η₆₀ /η₅ is less than 0.5,that is to say the tendency to viscosity decrease exceeds the allowablerange, long-run molding results in the deposition of burned resin aroundthe die, infiltration of gels, formation of fish eyes, coloration onaging and other product defects as well as molding instability in themanufacture of a strand or film. If η₆₀ /η₅ exceeds 4, that is to saythe tendency toward viscosity gain exceeds the allowable range, long-runmolding results in the deposition of burned resin around the die,infiltration of gels, formation of fish eyes and other product defects.Thus, in either case, the long-run molding operation is made difficult.

The melt viscosity mentioned above is the value determined with a Kokatype flow tester using a 1 mm φ×10 mm nozzle and a load of 10 kg/cm².The values η₅, η₆₀ are found by measuring the viscosities at theresidence times in the cyclinder of 5 and 60 minutes at a temperature of250° C.

Such saponified ethylene-vinyl acetate copolymer varies its propertiesaccording to the polymerization method, saponification method, degree ofpolymerization, degree of saponification, treatment followingsaponification, drying conditions, additives, etc. and the method ofproduction cannot be defined in general terms. Typically, however, itcan be obtained by saponifying an ethylene-vinyl acetate copolymerhaving the above-defined ethylene content with alkali and purifying theresulting saponified ethylene-vinyl acetate copolymer powder, grains orpellets by washing. In this purification by washing, the resin isthoroughly washed with an aqueous solution of acid, especially of a weakacid, or a dilute aqueous solution of a strong acid or an acidic saltthereof and, if necessary, further rinsed to remove the acid attached tothe resin, followed by drying.

The weak acid which can be used as above generally includes acids havingpKa (25° C.) values of not less than 3.5, such as acetic acid, propionicacid, glycolic acid, lactic acid, adipic acid, azelaic acid, glutaricacid, succinic acid, benzoic acid, isophthalic acid, terephthalic acidand so on. It is possible and preferable to further treat the resin witha dilute strong acid, e.g. an aqueous solution of an organic acid havinga pKa (25° C.) value of not more than 2.5, such as oxalic acid, maleicacid, etc., an inorganic acid such as phosphoric acid, sulfuric acid,nitric acid, hydrochloric acid, etc. or an acidic salt thereof before orafter aqeuous rinse following said treatment with a weak acid.

When the η₆₀ /η₅ values of commercial saponified ethylene-vinyl acetatecopolymers are investigated from the above standpoint of meltcharacteristics, they are found to vary a great deal from one showing atendency toward viscosity gain to one showing a tendency towardviscosity drop, indicating that no attention has heretofore been paid toη₆₀ /η₅.

The saponified ethylene-vinyl acetate copolymer can also be obtained asone having a water content of 20 to 60 weight % according to conditionsof production. The compatibility of such a copolymer with thestarch-based macromolecular substance is superior and can be smoothlymelt-molded even without use of a plasticizer or with a reduced amountof the plasticizer. However, an excessive water content should beavoided, for otherwise foaming may take place in melt-molding tointerfere with smooth molding or the surface characteristics of moldingswill be adversely affected. Typically such a saponified ethylene-vinylacetate copolymer can be prepared by adding water to a methanolicsolution of the saponified ethylene-vinyl acetate copolymer obtained byalkali saponification of an ethylene-vinyl acetate. copolymer to give asolution in the mixed solvent of water-methanol, introducing thissolution into water for coagulation, pelletizing or crushing thecoagulate, and purifying the same by washing. In the purification bywashing, it is preferable, just as described before, to wash the resinthoroughly with acid, particularly an aqueous solution of a weak acid ora dilute aqueous solution of an acidic salt of a strong acid, removingthe acid attached to the resin by rinsing, and drying the resin underconditions conducive to the desired water content.

Starch-based macromolecular substance

The starch-based macromolecular substance includes raw starches such ascorn starch, potato starch, sweet potato starch, wheat starch, cassavastarch, sago starch, tapioca starch, sorghum starch, rice starch, legumestarch, arrowroot starch, bracken starch, Indian lotus starch, waterchestnut starch, etc.; physically modified starch (a-starch,fractionated amylose, wet heat-treated starch, etc.), enzymaticallymodified starch (hydrolyzed dextrin, enzymatically degraded dextrin,amylose, etc.); chemically degraded and modified starch (acid-treatedstarch, hypochlorite-oxidized starch, dialdehyde starch, etc.);chemically modified starch derivatives (esterified starch, etherizedstarch, cationized starch, crosslinked starch, etc.) and so on. Amongsaid chemically modified starch derivatives, esterified starch includesacetic acid-esterified starch, succinic acid-esterified starch, nitricacid-esterified starch, phosphoric acid-esterified starch, ureaphosphoric acid-esterified starch, xanthic acid-esterified starch,acetoacetic acid-esterified starch, etc. The etherized starch includesallyl-etherized starch, methyl-etherized starch, carboxymethyl-etherizedstarch, hydroxyethyl-etherized starch, hydroxypropyl-etherized starch,etc. The cationized starch includes the reaction product between starchand 2-diethylaminoethyl chloride and the reaction product between starchand 2,3-epoxypropyltrimetylammonium chloride, etc. The crosslinkedstarch includes formaldehyde-crosslinked starch,epichlorohydrin-crosslinked starch, phosphoric acid-crosslinked starch,acrolein-crosslinked starch and so on.

In the practice of the present invention the starch-based macromolecularsubstance can be used in hydrated state and the proper water content inthat case may for example be 8 to 30 weight %. Then, coloration,burning, charring and contamination with foreign matter may bealleviated.

Proportions

The ratio of saponified ethylene-vinyl acetate copolymer to starch-basedmacromolecular substance is preferably 80:20 through 20:80, w/w, andmore preferably 70:30 through 30:70, w/w. If the proportion ofstarch-based macromolecular substance is too small, the biodegradabilityand disintegratability will be poor, while an excessive proportion ofthe substance detracts from the mechanical properties of moldings.However, depending on applications, some derivation from the above ratiocan be tolerated.

Additives

While the resin composition of the present invention is essentiallycomposed of said saponified ethylene-vinyl acetate copolymer andstarch-based macromolecular substance, it may contain as necessary avariety of additives such as plasticizers (e.g. polyhydric alcohols,urea, etc.), resin components (e.g. ethylene copolymers and otherpolyolefins, hydrogenated styrene-butadiene rubber, polyurethane,polyamide, polyhydroxybutyrate, etc.), natural polymers other than thoserelated to starch (polysaccharide type polymers, cellulosic polymers,proteinaceous polymers, etc.), heat stabilizers, diluents, autoxidants,fillers, lubricants, colorants, flame retardants, waterproofing agents,ultraviolet absorbers, crosslinking agents, fungicides, herbicides,antioxidants and so on. As starch modifiers, urea, alkaline earth oralkali metal hydroxides or mixtures thereof can also be added.

It is particularly instrumental to incorporate a polyhydric alcohol,such as glycerin, trimethyolpropane, pentaerythritol, ethylene glycol,diethylene glycol, triethylene glycol, propylene glycol, dipropyleneglycol, polypropylene glycol, etc. as well as urea. The amount of suchplasticizer can be optionally selected.

In the practice of the invention, the polyhydric alcohol preferably has2 to 4 hydroxyl groups and melts at a temperature not below 40° C.,preferably between 40° and 150° C., and has a molecular weight of notmore than 600, preferably between 100 and 300. Among examples of suchpolyhydric alcohol are dihydric alcohols such as 1,6-hexanediol,1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, neopentyl glycol,hydrobenzoin, 1,2-cyclohexanedimethanol, etc.; trihydric alcohols suchas trimethylolpropane, trimethylolethane, etc.; and tetrahydric alcoholssuch as pentaerythritol. Among them, 1,6-hexanediol, neopentyl glycol,1,4-cyclohexanedimethanol, and trimethylolpropane are preferred frompractical points of view. The proportion of such polyhydric alcohol is 5to 50 parts by weight, preferably 10 to 40 parts by weight, based on 100parts by weight of the sum of said saponified ethylene-vinyl acetatecopolymer and starch-based macromolecular substance. If the proportionis less than 5 parts by weight, the effect will not be sufficient, whilea proportion of more than 50 parts by weight will not insure acommensurate effect but rather detract from mechanical strength to makethe composition unpractical.

Melt-molding technology

As the melt-molding technology, extrusion molding (inclusive of blowmolding) can be mainly utilized. However, calendering and injectionmolding processes can also be employed. The preferred extrusion moldingprocess comprises feeding the saponified ethylene-vinyl acetatecopolymer and the starch-based macromolecular substance eitherindependently or concurrently to an extruder for melt-mixing andpelletization and feeding the resulting pellets to an extruder formolding to the desired shape. The melt-forming temperature in the latterstage is often set to a temperature not exceeding 180° C. When thestarch-based macromolecular substance or the saponified ethylene-vinylacetate copolymer is hydrous or when the molding operation is performedwith addition of water, it is preferable to reduce the water content ofthe extrudate to 5 weight % or less using an extruder equipped with avent means before feeding to the latter stage extruder for melt-molding.

When the melt-molding is carried out by extrusion molding, it isgenerally preferable to set the resin temperature at the joint betweenthe extruder and the die to 170° C. or below and the shear rate of themelt passing through the die lip to not less than 100 sec⁻¹.

In molding, it is also possible to employ a special mixing mode suchthat the saponified ethylenevinyl acetate copolymer and the starch-basedmacromolecular substance are independently melted beforehand and, then,blended in molten state. According to this mode, there can bemanufactured a shaped product of improved quality with reducedincidences of discoloration associated with thermal degradation, fisheyes, grains, gelation and burn. In this case, a plasticizer may beincorporated but its-proportion need not be greater than, for example,10 parts by weight relative to 100 parts by weight of the sum ofsaponified ethylene-vinyl acetate copolymer and starch-basedmacromolecular substance. Regarding the above mode in which thesaponified ethylene-vinyl acetate copolymer melted by heating beforehandis blended with the starch-based macromolecular substance similarlymelted beforehand, an exemplary process comprises melting thestarch-based macromolecular substance in a twin-screw extruder in thefirst place and feeding the saponified ethylenevinyl acetate copolymerfrom a side feed port of the same twin-screw extruder for mixing to givea homogeneous blend. For the manufacture of shaped products, it ispreferable to pelletize the blend thus obtained and feed the pellets toan extruder for molding to the desired shape.

Laminate

In accordance with the present invention, a layer composed of such acomposition comprising the saponified ethylene-vinyl acetate copolymerand starch-based macromolecular substance can be laminated with a layercomposed of a different substrate material. The different materialmentioned just above may for example be a thermoplastic resin, kraft orother paper, woven cloth, nonwoven cloth, metal foil or wood board.

The thermoplastic resin includes, among others, polyolefin resin, vinylalcohol resin, acrylic resin, polyamide resin, polyester resin,polyurethane resin, polystyrene resin, polyacetal resin, polycarbonateresin, diene type resin, cellulosic resin and so on. When, among thesethermoplastic resins, particularly one or more photodegradable polymersselected from the group consisting of ethylene-CO copolymer,ethylenevinyl ketone copolymer, polybutadine and isoprene rubber or apolyolefinic photodegradable polymer containing at least one of theseresins as blended, or even a photodegradable polymer renderedphotodegradable by incorporation of a transition metal or aphotosensitizer is employed as said different material for laminationwith the layer comprised of the composition of the invention which isper se biodegradable, the resulting laminate as a whole is naturallydisintegratable. The laminate obtainable by using a paper, a naturalcellulose-based woven or nonwoven cloth, a wooden board or the like isalso biodegradable and disintegratable. Therefore, an increasedindustrial usefulness can then be attained.

The ethylene-CO copolymer can be obtained by copolymerizing ethylenewith CO at high temperature and super-high pressure and thecopolymerizing rate of CO is generally about 0.3 to 10 weight %. Theethylenevinyl ketone copolymer includes ethylene-methyl vinyl ketonecopolymer and ethylene-phenyl vinyl ketone copolymer, to name but a few.The copolymerizing proportion of vinyl ketone is generally about 0.1 to10 mole % but may be higher. The polybutadiene includes thermoplastic1,2-polybutadiene, high cis-butadine and low cis-butadiene rubbers, toname but a few. Particularly preferred is a thermoplastic1,2-polybutadiene with 90% of butadiene units forming 1,2-bonds. Theisoprene rubber includes natural rubber, isoprene rubber,trans-polyisoprene, etc. and, among them, natural rubber is particularlyimportant.

It is also possible to employ a photodegradable polymer prepared byblending 3 to 20 parts by weight of any of said ethylene-CO copolymer,ethylene-methyl vinyl ketone copolymer, ethylene-phenyl vinyl ketonecopolymer, 1,2-polybutadiene, etc. with 100 parts by weight of apolyolefin such as a low-density polyethylene, linear low-densitypolyethylene, high-density polyethylene, polypropylene, ethylene-vinylacetate polymer or the like. It is also possible to employ aphotodegradable polymer whose photodegradability has been imparted by atransition metal salt or a photosensitizer.

As the transition metal salt, these can be employed salts of stearine,dialkylthiocarbamates, salicylaldehyde, acetylacetone benzophenoneoxime, etc. with iron(II), zinc(II), manganese(II), nickel(II),cerium(III), cobalt(II) or the like. The photosensitizer may for examplebe benzophenone, acetophenone or anthraquinone.

For laminating a layer comprised of the above composition with a layercomprised of said different material, any of the known methods such asdry lamination, extrusion, co-injection, multi-layer inflation,multi-layer T-die extrusion, multi-layer blow molding, multi-layer pipeextrusion, etc. can be invariably employed. As to the bonding mode ofmolten resin, whichever of "in-die" bonding and "out-of-die" bonding canbe employed.

In manufacturing such a laminate by melt-molding, an adhesive can beemployed with advantage. For the adhesive layer, a variety of adhesivessuch as polyolefin, polyester, acrylic and other adhesives can besuccessfully utilized. Preferably, acid-modified polyolefins, and morepreferably carboxylic acid (e.g. maleic anhydride)-modifiedpolypropylene, carboxylic acid-modified ethylene-vinyl acetate copolymeradhesives are employed. Such an adhesive layer is generally used in athickness of 5 to 50 μm. As the anchor coating agent for dry lamination,isocyanate, polyethyleneimine, polybutadiene, organotitanium and othercoating agents can be advantageously employed and the coating thicknessis generally 0.5 to 2 μm.

Other

The photodegradable polymer mentioned hereinbefore may be incorporatedin a composition comprising said saponified ethylene-vinyl acetatecopolymer and starch-based macromolecular substance. The proportion ofthe photodegradable polymer for this purpose is generally 3 to 70 partsby weight based on 100 parts by weight of the sum of saponifiedethylene-vinyl acetate copolymer and starch-based macromolecularsubstance.

Operation and Result

The present invention employs a saponified ethylene-vinyl acetatecopolymer having a definite melt characteristic, that is to say onehaving the specified melt viscosity ratio η₆₀ /η₅, where η₆₀ means themelt viscosity after 60 minutes of standing at 250° C. and η₅ means themelt viscosity after 5 minutes of standing at 250° C., so that despiteit being a binary system comprising a saponified ethylene-vinyl acetatecopolymer and a starch-based macromolecular substance, the acceptablemelt moldability and particularly long-run moldability which are thelong-standing problems to be solved are remarkably improved. Therefore,the invention permits a stable supply of biodegradable shaped productsin this binary system.

Furthermore, when a polyhydric alcohol containing 2 to 4 hydroxyl groupswithin the molecule and having a melting point of not lower than 40° C.and a molecular weight of not more than 600 is employed as theplasticizer, molding compatibility is very satisfactory and films ofexcellent clarity and flexibility can be manufactured. Moreover,bleeding of the plasticizer can also be avoided.

When a hydrous saponified ethylene-vinyl acetate copolymer with a watercontent of 20 to 60 weight % is employed as said saponifiedethylene-vinyl acetate copolymer, satisfactory moldability is assuredeven if addition of the plasticizer is omitted or the amount of theplasticizer is drastically reduced.

Furthermore, when the saponified ethylene-vinyl acetate copolymer andthe starch-based macromolecular substance are independently meltedbeforehand and blended in molten state, satisfactory melt-moldingresults can be obtained even with a reduced amount of the plasticizer.

Laminating a layer composed of the above composition with a substratelayer (particularly a layer composed of at least one photodegradablepolymer selected from the group consisting of ethylene-CO copolymer,ethylene vinyl ketone copolymer, polybutadiene and isoprene rubber or apolyolefin-based photodegradable polymer blend containing at least oneof said polymers) is useful in that it broadens the scope ofapplicability.

BEST MODE FOR CARRYING OUT THE INVENTION

The following examples are intended to describe the invention in furtherdetail.

Examples 1˜5, Comparative Examples 1˜5 Production of saponifiedethylene-vinyl acetate copolymers

To a methanolic solution of an ethylene-vinyl acetate copolymer havingan ethylene content of 44 mole 38 mole %, 32 mole % or 29 mole % wasadded sodium hydroxide, as the catalyst, for primary saponification andthe resulting preliminary hydrolysate was dispersed in water. Then, afurther amount of sodium hydroxide was added for secondarysaponification to obtain a saponified ethylene-vinyl acetate copolymerhaving a saponification degree of 99 mole %. This hydrolysate was rinsedwith water and, where necessary, washed with a dilute aqueous solutionof acetic acid or sodium phosphate, followed by drying. In this manner,saponified ethylene-vinyl acetate copolymers having the characteristicvalues indicated hereinafter in Table 1 were obtained.

Melt-molding and evaluation of long-run moldability

Each of the saponified ethylene-vinyl acetate copolymers obtained abovewas fed to a twin-screw extruder via its main feeder at a rate of 3kg/hr. At the same time, a mixture of 100 parts by weight of starch(corn starch) and 30 parts by weight of glycerin was fed to the abovetwin-screw extruder via its side feeder at a rate of 4 kg/hr. The strandextruded through the die was pelletized with a pelletizer to givepelllets 3 mm in diameter and 3 mm in length. The temperature settingsof the twin-screw extruder were as follows.

    ______________________________________                                        C.sub.1                                                                             C.sub.2 C.sub.3  C.sub.4                                                                             C.sub.5                                                                              H     D                                   ______________________________________                                        200° C.                                                                      170° C.                                                                        160° C.                                                                         160° C.                                                                      160° C.                                                                       160° C.                                                                      160° C.                      ______________________________________                                    

This pelletizing operation was continued for 3 consecutive days (1 or 2days in Comparative Examples) and the incidences of deposition of burnedresin near the discharge port of the twin-screw extruder, infiltrationof gels into the pellet, and the degree of pellet discoloration wereinvestigated. After completion of the above continuous molding, thetwin-screw extruder was disassembled and inspected for residues ofdegradation products.

Then, the above pellets (those obtained up to 3 hours after thebeginning of pelletization) were fed to a single-screw extruder forrepelletizing and this cycle was repeated for a total of 6 times. Thefinal pellets were fed to a single-screw extruder equipped with a T-dieto give a 30 μm thick film and the infiltration of gels into the filmand the incidence of fish eye were investigated. Moreover, the extruderused for the production of film was disassembled and inspected forinternal residues of degradation products.

In the above procedure, the single-screw extruder for pelletization andthe single-screw extruder for film formation were set to the followingtemperatures.

    ______________________________________                                        C.sub.1                                                                             C.sub.2 C.sub.3  C.sub.4                                                                             C.sub.5                                                                              H     D                                   ______________________________________                                        130° C.                                                                      160° C.                                                                        160° C.                                                                         160° C.                                                                      160° C.                                                                       160° C.                                                                      160° C.                      Single-screw extruder for film formation                                      C.sub.1                                                                             C.sub.2 C.sub.3  C.sub.4                                                                             C.sub.5                                                                              H     D                                   ______________________________________                                        130° C.                                                                      160° C.                                                                        160° C.                                                                         160° C.                                                                      160° C.                                                                       160° C.                                                                      160° C.                      ______________________________________                                    

Results

The results of evaluation of long-run molding performance are shownbelow in Table 1. The characteristic values of the saponifiedethylene-vinyl acetate copolymers used are also presented in Table 1.

                                      TABLE 1                                     __________________________________________________________________________               Example                     Comparative Example                               1   2    3   4    5   1     2     3     4     5                    __________________________________________________________________________    Characteristic values of EVOH                                                 Et content (mole %)                                                                      44  44   38  32   29  44    38    38    32    29                   SV (mole %)                                                                              99  99   99  99   99  99    99    99    99    99                   MFI (g/10 min)                                                                           12  12   25  3    8   12    8     25    3     8                    η.sub.60 /η.sub.5                                                                1.2 0.9  2.2 2.5  2.0 4.9   5.5   0.1   5.2   0.3                  Long-run moldability with a twin-screw extruder                               Number of days of                                                                        3   3    3   3    3   1     1     2     1     2                    continuous molding                                                            Burnt resin deposits                                                                     None                                                                              None None                                                                              Slight                                                                             None                                                                              Abundant                                                                            Abundant                                                                            Abundant                                                                            Abundant                                                                            Abundant             Gels       None                                                                              None None                                                                              None None                                                                              Abundant                                                                            Abundant                                                                            Obvious                                                                             Abundant                                                                            Obvious              Coloration on aging                                                                      None                                                                              Minimal                                                                            None                                                                              None None                                                                              Minimal                                                                             Minimal                                                                             Obvious                                                                             None  Obvious              Degradation product                                                                      None                                                                              None None                                                                              Minimal                                                                            None                                                                              Abundant                                                                            Abundant                                                                            Abundant                                                                            Abundant                                                                            Obvious              residues                                                                      (Disassembling                                                                           ∘                                                                     ∘                                                                      ∘                                                                     ∘                                                                      ∘                                                                     x     x     x     x     Δ              inspection)                                                                   Overall evaluation                                                            Film formation after 6 pelletizing cycles                                     Gels       None                                                                              None None                                                                              None None                                                                              Abundant                                                                            Abundant                                                                            Abundant                                                                            Abundant                                                                            Obvious              Fish eyes  None                                                                              None None                                                                              None None                                                                              Abundant                                                                            Abundant                                                                            Abundant                                                                            Abundant                                                                            Abundant             Degradation product                                                                      None                                                                              None None                                                                              Minimal                                                                            None                                                                              Abundant                                                                            Abundant                                                                            Abundant                                                                            Abundant                                                                            Abundant             residues                                                                      (Disassembling                                                                           ∘                                                                     ∘                                                                      ∘                                                                     ∘                                                                      ∘                                                                     x     x     x     x     x                    inspection)                                                                   overall evaluation                                                            __________________________________________________________________________     (Note)                                                                        The symbols used in Table 1 have the following meanings.                      EVOH: saponified ethylenevinyl acetate copolymer                              Et content: ethylene content                                                  Sv: saponification degree                                                     MFI: melt flow index                                                          η.sub.60 /η.sub.5 : melt viscosity ratio                              (Note)                                                                        In Table 1, the degrees of burnt resin deposit, gel infiltration,             coloration on aging and fish eye were respectively evaluated on the 5grad     scale of none, minimal, slight, obvious and abundant.                    

The overall evaluation was made on the 3-grade scale of o (good), Δ(fair) and x (poor).

Examples 6˜10 Production of saponified ethylene-vinyl acetate copolymers

Each of ethylene-vinyl acetate copolymers varying in ethylene contentwas saponified, rinsed, washed with a dilute solution of acetic acid anda dilute aqueous solution of phosphoric acid, further rinsed and driedin the conventional manner.

The compositions, melt flow indices (MFI) and melt viscosity ratios ofthe resulting saponified ethylenevinyl acetate copolymers are shownbelow in Table 2.

Compound pelletization

A Henschel mixer was charged with pellets of a saponified ethylene-vinylacetate copolymer obtained above, raw starch (corn starch with a watercontent of 12 weight %, an example of the starch-based macromolecularsubstance), and a plasticizer in the proportions and combination shownin Table 2. After mixing, the mixture was fed to a twin-screw extruderequipped with vent means and melt-extruded into a strand and, at thesame time, pelletized with a pelletizer to give a pelleted resincomposition. The temperature settings of the twin-screw extruder were asshown below.

    ______________________________________                                        Screw diameter   30 mm                                                        L/D              30                                                           Screw RPM       150 rpm (unidirectional rotation)                             Vent            Open vent                                                     Die             Two nozzles, 5 mm in diameter                                 ______________________________________                                        Temperature settings                                                          C.sub.1                                                                             C.sub.2 C.sub.3  C.sub.4                                                                             C.sub.5                                                                              H     D                                   ______________________________________                                        100° C.                                                                      140° C.                                                                        160° C.                                                                         160° C.                                                                      160° C.                                                                       160° C.                                                                      160° C.                      ______________________________________                                    

The resulting pellets were hot-pressed under the conditions of 150°C.×50 kgf/cm² ×5 minutes to mold a mm-thick plate. To evaluate theclarity of the plate, the total light transmittance of the hot-pressedplate was measured in accordance with JIS K7105.

Film production

The above compound pellets were fed to a single-screw extruder equippedwith a T-die to mold a 50 μm-thick film. The film-forming conditions ofthe single-screw extruder were as follows.

    ______________________________________                                        Screw diameter   40 mm                                                        L/D              28                                                           Screw RPM        50 rpm (unidirectional rotation)                             Screw configuration                                                                           Full flight                                                   Compression ratio                                                                              3.0                                                          T-die           Coat hanger type                                              Die width       450 mm                                                        Die lip opening  0.5 mm                                                       ______________________________________                                        Temperature conditions                                                        C.sub.1                                                                             C.sub.2   C.sub.3 C.sub.4 H     D                                       ______________________________________                                        140° C.                                                                      160° C.                                                                          160° C.                                                                        160° C.                                                                        160° C.                                                                      160° C.                          ______________________________________                                    

Bleeding test

The above film was sandwiched between strips of filter paper and allowedto stand at 20° C. and 65% RH. The staining of the filter paper due tobleeding of the plasticizer was investigated by washing the filter paperafter standing with methyl alcohol and measuring the infrared absorptionspectrum of a concentrate of the washing.

Biodegradability

The above film was cut to B5 size (25.8 mm×18.2 mm) and buried in acompost-soil mixture. After 6 months, the film was taken out andvisually inspected and evaluated according to the following criteria.

a: Only residual fragments can be confirmed and no shape of the originalfilm is retained.

b: The original shape is retained but a multiplicity of cracks andopenings are observed all over.

Results

The results as well as the formulations are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                  Example                                                                       6      7       8       9     10                                     ______________________________________                                        Characteristic values of EVOH                                                 Et content    44.2     49.0    38.2                                                                                28.9                                                                                44.1                               (mole %)                                                                      SV (mole %)   99.5     99.2    99.4                                                                                99.3                                                                                96.0                               MFI (g/10 min)                                                                            12       15      25     8    13                                   η.sub.60 /η.sub.5                                                                   0.9      2.6     2.2   2.0   0.9                                Plasticizer NPG      CHD     HD    TMP   PE                                   Molecular weight                                                                          104      144     118   134   136                                  Melting point (°C.)                                                                128-130  45-50   43    59    260                                  Formula (parts)                                                               EVOH        40       35      45    50    55                                   Raw starch  60       65      55    50    45                                   Plasticizer 20       15      25    30    40                                   Pelletizability                                                                           Good     Good    Good  Good  Good                                 Total light 75       78      82    76    74                                   transmittance (%)                                                             Modulus in tension                                                                        6300     4800    5100  6600  9000                                 (kgf/cm )                                                                     Film formability                                                                          Good     Good    Good  Good  Good                                 Bleeding    None     None    None  None  None                                 Biodegradability                                                                          a        a       a     a     a                                    ______________________________________                                         (Note)                                                                        The abbreviations in the plasticizer column mean the following.               NPG: neopentyl glycol                                                         CHD: 1,4cyclohexanedimethanol                                                 HD: 1,6hexanediol                                                             TMP: trimethylolpropane                                                       PE: pentaerythritol                                                      

Reference Examples 1˜2, Comparative Examples 6˜7

The procedures of Examples 6˜10 were repeated except that the compoundsindicated below in Table 3 were used as the plasticizer. The results areset forth in Table 3.

                  TABLE 3                                                         ______________________________________                                                   Reference   Comparative                                                       Example     Example                                                           1      2        6        7                                         ______________________________________                                        Characteristic values of EVOH                                                 Et content (mole %)                                                                         44.2     49.0      38.2   28.9                                  SV (mole %)   99.5     99.2      99.4   99.3                                  MFI (g/10 min)                                                                              12       15        25     8                                     η.sub.60 /η.sub.5                                                                    0.9      2.6      0.1    0.3                                   Plasticizer  Gly      L-PEG    H-PEG  SB                                      Molecular weight                                                                            92       300      4000   182                                    Melting point (°C.)                                                                  18      -15˜6                                                                             53˜56                                                                           97                                    Formula (parts)                                                               EVOH          40       35        45     50                                    Raw starch    60       65        55     50                                    Plasticizer   20       15        25     30                                    Pelletizability                                                                            Good     Good     Good   Good                                    Total light   80       78        0      80                                    transmittance (%)                                                             Modulus in tension                                                                         5600     5200     12000  30000                                   (kgf/cm.sup.2)                                                                Film formability                                                                           Good     Good     Poor   Poor                                    Bleeding     Observed Observed --     --                                      Biodegradability                                                                           b        b        --     --                                      ______________________________________                                         (Note)                                                                        The abbreviations in the plasticizer column mean the following.               Gly: glycerin                                                                 LPEG: low molecular weight polyethylene glycol                                HPEG: high molecular weight polyethylene glycol                               SB: sorbitol                                                                  (Note)                                                                        In the pelletizability column, "poor" means a difficulty in takeup of the     strand.                                                                  

In the film formability column, "poor" means a difficulty in theformation of film.

Therefore, the bleeding and biodegradability parameters in ComparativeExamples 6 and 7 were not determined.

Examples 11˜15 Production of saponified ethylene-vinyl acetatecopolymers

To a methanolic solution of an ethylene-vinyl acetate copolymers varyingin ethylene content was added a methanolic solution of sodium hydroxideas the catalyst and a continuous saponification reaction was conductedin a reactor. The resulting solution of the saponified copolymer inmethanol was diluted with water to prepare a mixed solution in methanoland water and the dilution was discharged from a nozzle into water at atemperature not exceeding 20° C. Thereupon the solution becamecoagulated in a strand form with a diameter of about 3 mm. The coagulatewas taken out from the water and cut.

The coagulated strand was pelletized with a pelletizer, rinsed to removesodium acetate from the polymer, washed with a dilute aqueous solutionof acetic acid and further with a dilute aqueous solution of phosphoricacid and dried under varying drying conditions to adjust to the targetwater content.

The characteristic values, water contents, and melting points (DSC peaktemperatures) in hydrous state of the resulting hydrous saponifiedethylene-vinyl acetate copolymers are shown in Table 4.

Pelletization of compound

A Henschel mixer was charged with pellets of the above hydrousethylene-vinyl acetate copolymer and raw starch (corn starch with awater content of 12 weight in the proportions and combination indicatedin Table 4. After mixing, the mixture was fed to a twin-screw extruderwith vent means and melt-extruded in the form of a strand and pelletizedwith a pelletizer. The operating parameters of the twin-screw extruderwere as follows.

    ______________________________________                                        Screw diameter   30 mm                                                        L/D              30                                                           Screw RPM       150 rpm                                                       Vent            open vent                                                     Die             Two nozzles, 3.0 mm in diameter                               ______________________________________                                        Temperature settings                                                          C.sub.1                                                                             C.sub.2 C.sub.3  C.sub.4                                                                             C.sub.5                                                                              H     D                                   ______________________________________                                        50° C.                                                                       110° C.                                                                        120° C.                                                                         120° C.                                                                      120° C.                                                                       120° C.                                                                      120° C.                      ______________________________________                                    

Melt-molding

The compound pellets obtained as above were fed to an injection moldingmachine with a cramping pressure of 100 tons and injection-molded underthe following conditions to fabricate a sheet (flat) sized 100 mm×100mm×1.5 mm (thickness), a No. 1 tensile test-piece according to JISK-7113, and a flexure test-piece according to JIS K-2703.

    ______________________________________                                        Injection pressure                                                                             200 kg/cm.sup.2                                              Injection speed  High pressure setting                                        Mold             A flat sheet mold of fan gate                                                 type, side gate No. 1                                                         Tensile testpiece mold and                                                    flexure testpiece mold                                       Mold temperature 40° C.                                                ______________________________________                                        Temperature conditions                                                        C.sub.1 C.sub.2      C.sub.3   Nozzle                                         ______________________________________                                        100° C.                                                                        110-140° C.                                                                         110-140° C.                                                                      110-140° C.                             ______________________________________                                    

Results

The results as well as the conditions used are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                                   Example                                                                       11    12      13      14    15                                     ______________________________________                                        Characteristic values of EVOH                                                 Et content (mole %)                                                                        44.0    44.0    44.0  38.0  29.0                                 SV (mole %)  99.5    99.5    99.5  99.5  99.5                                 MFI (g/10 min)                                                                             12      12      12    25    8                                    η.sub.60 /η.sub.5                                                                  0.9     0.9     0.9   2.2   2.0                                  Water content (wt %)                                                                       53      53      26    30    55                                   Melting point in                                                                           96      96      100   98    93                                   hydrous state (°C.)                                                    Formula (parts)                                                               Hydrous EVOH 150     100     100   100   160                                  Raw starch   100     100     100   100   100                                  Pelletizability                                                                            Good    Good    Good  Good  Good                                 Pellet composition (wt %)                                                     EVOH         33      26      40    38    34                                   Raw starch   42      50      47    48    41                                   Water        25      24      13    14    25                                   Injection molda-                                                                           Good    Good    Good  Good  Good                                 bility of pellet                                                              Mechanical strengths                                                          Tentile strength                                                                           240     300     350   360   260                                  (kg/cm.sup.2)                                                                 Elongation (%)                                                                             50      40      40    35    40                                   Flexural strength                                                                          220     280     350   350   250                                  (kg/cm.sup.2)                                                                 Bleeding     None    None    None  None  None                                 Biodegradability (disintegratability)                                         Six months   b       b       b     b     b                                    One year     a       a       a     a     a                                    ______________________________________                                         (Note)                                                                        In the pelletizability column, "good" means satisfactory blending and goo     takeup of the strand.                                                    

The mechanical strengths were measured at 20° C. in accordance with JISK-7113 (tensile test) and JIS K-2703 (flexure test).

For the evaluation of biodegradability (disintegratability), the flatsheet samples obtained as above were buried in a compost-soil mixtureand 6 months and one year later were taken out and visually examined andscored on the following 3-grade scale.

a: Not less than 50% by volume of the sample has lost shape.

b: The entire surface of the sample has been corrugated and the fouredges are also indented, indicating that disintegration is in progress.

c: Recessed spots are locally found on the surface and edges of thesample

Film production Examples 1˜4 Production of hydrous saponifiedethylene-vinyl acetate copolymers

The hydrous saponified ethylene-vinyl acetate copolymers indicated inTable 5 were prepared in the same manner as Examples 11˜15.

Production of films from compositions

A Henschel mixer was charged with pellets of the above hydrousethylene-vinyl acetate copolymer, raw starch (corn starch with a watercontent of 12 weight and, as necessary, glycerin in the proportions andcombinations shown in Table 5. The mixture was then fed to a twin-screwextruder equipped with vent means and melt-extruded into a strand at120° C. and pelletized with a pelletizer.

The resulting pellets were fed to a single-screw extruder and extrudedthrough a T-die at a cylinder temperature of not higher than 140° C. anda die temperature of not higher than 140° C. to prepare a 35 μm-thickfilm, The film was passed through a hot-current circulating dryingfurnace at 150° C. to adjust the water content of the film to not morethan 7%,

Production of films

The materials mentioned in each Example were fed in the indicatedproportions to a single-screw extruder and extruded from a T-die at acylinder temperature of 200° to 230° C. and a die temperature of 200° to230° C. to prepare a 50 μm-thick film.

Conditions and Results

Pelletizability ratings, compositions and film-forming properties areshown in Table 5.

                  TABLE 5                                                         ______________________________________                                                       Film production Example                                                       1     2       3       4                                        ______________________________________                                        Characteristic values of EVOH                                                 Et content (mole %)                                                                            44.2    27.8    38.2  46.8                                   SV (mole %)      99.5    99.5    99.4  99.2                                   MFI (g/10 min)   12      8       25    14                                     η.sub.60 η.sub.5                                                                       0.9     2.0     2.2   1.0                                    Water content (wt %)                                                                           26      40      35    40                                     Melting point in 100     95      97    93                                     hydrous state (°C.)                                                    Formula (parts)                                                               Hydrous EVOH     67.6    108.3   84.6  58.3                                   Raw starch       56.8    39.8    51.1  73.9                                   Glycerin         --      --      --    19                                     Pelletizability  Good    Good    Good  Good                                   Pellet composition (wt %)                                                     EVOH             42.1    46.6    42.2  25.6                                   Raw starch       42.1    25.1    34.6  47.4                                   Water            15.8    28.3    23.2  20.2                                   Glycerin         --      --      --    6.8                                    Dry weight ratio of                                                                            50/50   35/65   55/45 65/35                                  raw starch to EVOH                                                            Film-forming     Good    Good    Good  Good                                   property                                                                      Film code number F-1     F-2     F-3   F-4                                    ______________________________________                                    

Fabrication of laminates Examples 16˜19

Using an isocyanate anchor coating agent (D), the above film (F-1),(F-2), (F-3) or (F-4) was dry-laminated with the following substratefilm (C-1), (C-2), (C-3) or (C-4) to fabricate a laminate with the layerthicknesses (μm) of (F)/(D)/(C)=35/1/50.

(C-1): an ethylene-CO copolymer film

(C-2): a low-density polyethylene film blended with 10 weight % of anethylene-methyl vinyl ketone (5 mole %) copolymer

(C-3): a high-density polyethylene film blended with 10 weight % of athermoplastic 1,2-polybutadiene

(C-4): a linear low-density polyethylene film containing 0.5 weight % offerric stearate

The laminar structures and measured data are shown in Table 6.

                  TABLE 6                                                         ______________________________________                                                       Example                                                                       16   17       18     19                                        ______________________________________                                        Laminar structure                                                             Film (F)         F-1    F-2      F-3  F-4                                     Base film (C)    C-1    C-2      C-3  C-4                                     Oxygen permeability                                                           (cc/m.sup.2 · 24 hr · atm)                                  25° C., 30% RH                                                                          0.5    0.3      0.4  1.5                                     25° C., 75% RH                                                                          1.5    1.0      1.7  7.3                                     Interlayer bond strength                                                                       850    830      760  530                                     (g/25 mm wide)                                                                Natural disintegratability                                                                     Yes    Yes      Yes  Yes                                     on soil                                                                       ______________________________________                                         (Note)                                                                        Oxygen permeability was measured in accordance with ASTM D 3985 at            25° C., 30% RH and 75% RH using Modern Control's OXTRAN 100.      

The interlayer bond strength was measured between film layer (F) andbase film layer (C) in accordance with JIS Z-0237.

As to disintegratability, a film sample 1 m×1 m was set with its filmlayer (F) in contact with the ground surface and the film was visuallyinspected after 6 months and one year. As a result, the films accordingto Examples 16˜19 showed formation of many cracks after 6 months and haddisintegrated completely out of shape by the end of one year.

Example 20

The above film (F-1) was laminated with a 30 μm-thick kraft paper byhot-pressing and the physical properties of the laminate weredetermined. The oxygen permeability was 0.5 cc/m² ·24 hr.atm at 25° C.,30% RH and 1.6 cc/m² ·24 hr-atm at 25° C., 75% RH. The interlayer bondstrength could not be measured because of breakage of the kraft paperduring determination. As to disintegratability, many cracks and holeswere found after 6 months and no shape was retained after 1 year.

Comparative Example 8

On a 50 μm-thick polyethylene film surfaced with an anchor coatingmaterial was formed a 35 μm-thick starch layer by the casting methodusing raw starch (corn starch with a water content of 12 weight %). Theoxygen permeability of this laminate film was 2.0 cc/m² ·24 hr.atm at25° C., 30% RH and 70 cc/m² ·24 hr-atm at 25° C., 75% RH. As tointerlayer bond strength, peeling occurred and the starch film waseasily broken at 0 g/25 mm width.

Comparative Example 9

A Henschel mixer was charged with 80 parts by weight of a low-densitypolyethylene with a melt index of 6 g/10 min. (Mitsubishi KaseiCorporation, F-161) and 20 parts by weight of raw starch (corn starchwith a water content of 12 weight %) and after blending, the mixture wasfed to an extruder for pelletization. The pellets were fed to anextruder and melt-extruded through a T-die at a cylinder temperature of190° C. and a die temperature of 180° C. to provide a 30 μm-thick film.When the proportion of raw starch was increased over the above value, nofilm could be produced.

Using an isocyanate anchor coating agent (D), the film obtained abovewas dry-laminated with a 30 μm-thick polyethylene film and the physicalproperties of the laminate were determined.

The oxygen permeability of this laminate film was not less than 1000cm/m² ·24 hr atm at 25° C., 30% RH and not less than 1000 cm/m² ·24hr-atm at 25° C., 75% RH. The interlayer bond strength was 850 g/25 mmwidth.

Examples 21˜27 Production of saponified ethylene-vinyl acetatecopolymers

An ethylene-vinyl acetate copolymer was saponified and washed in thesame manner as Examples 11-15 and dried to give the saponifiedethylene-vinyl acetate copolymers indicated below in Table 7.

                  TABLE 7                                                         ______________________________________                                                        E-1    E-2      E-3                                           ______________________________________                                        Characteristic values of EVOH                                                 Et content (mole %)                                                                             29.2     38.8     43.3                                      SV (mole %)       99.5     99.4     99.5                                      Melting point (°C.)                                                                      186      178      167                                       MFI (g/10 min)    8.2      25.4     12.1                                      η.sub.60 /η.sub.5                                                                       1.9      2.2      0.9                                       ______________________________________                                    

Compound pelletization

Starch and glycerin were admixed and the mixture was fed in apredetermined amount through a measuring feeder to a twin-screwextruder, in which it was melted by heating at 170° C. Then, asaponified ethylene-vinyl acetate copolymer prepared as shown in Table 7was fed in a predetermined amount through a measuring feeder to asingle-screw extruder and melted by heating at 210° C. The melt was fedto the above twin-screw extruder via its side feeding port. The twocharges were blended until a homogeneous blend was obtained. Theformulas are shown hereinafter in Table 8. The extruder parameters wereas follows.

    ______________________________________                                        Twin-screw extruder                                                           Screw diameter       30       mm                                              L/D                  30                                                       Screw RPM            120      rpm                                             Extrusion temperatures                                                                             C.sub.1   70° C.                                                       C.sub.2  160° C.                                                       C.sub.3  170° C.                                                       C.sub.4  170° C.                                                       C.sub.5  170° C.                                                       Adapter  170° C.                                                       Die      170° C.                                                       (Side feeder: C.sub.3)                                   Single-screw extruder                                                         Screw diameter       30       mm                                              L/D                  24                                                       Screw RPM            100      rpm                                             Extrusion temperatures                                                                             C.sub.1  210° C.                                                       C.sub.2  200° C.                                                       C.sub.3  210° C.                                                       Joint    210° C.                                  ______________________________________                                    

Production of films

The compound pellets obtained by 12-hr continuous extrusion asexternally supplemented with an aggregate (0.3 part ofethylenebisstearoidamide) was fed to a single-screw extruder equippedwith a T-die to prepare a 50 μm-thick film. The film-forming conditionsat the single-screw extruder were as follows.

    ______________________________________                                        Screw inside diameter                                                                              40 mm                                                    L/D                  28                                                       T-die               Coat hanger type                                          Die width           450 mm                                                    Die lip opening      0.5 mm                                                   Extrusion temperature                                                                             140-180° C.                                        ______________________________________                                    

                                      TABLE 8                                     __________________________________________________________________________               Example                                                                       21   22   23   24   25   26   27                                   __________________________________________________________________________    Formula                                                                       Twin-screw extruder                                                           Starch      70  120  120  200  120  200  300                                  (water content 12.8%)                                                         Glycerin    10   20   10   10   10   10   20                                  Single-screw extruder                                                         EVOH       E-1  E-1  E-2  E-2  E-3  E-3  E-3                                             100  100  100  100  100  100  100                                  Evaluation                                                                    Processability                                                                Surface of strand                                                                        Smooth                                                                             Smooth                                                                             Smooth                                                                             Smooth                                                                             Smooth                                                                             Smooth                                                                             Smooth                               Thermal coloration                                                                       Light                                                                              Light                                                                              Light                                                                              Light                                                                              Light                                                                              Light                                                                              Light                                of pellet  yellow                                                                             yellow                                                                             yellow                                                                             yellow                                                                             yellow                                                                             yellow                                                                             yellow                               Quality                                                                       Degree of granular                                                                       Good Good Good Good Good Good Good                                 structure                                                                     Tensile strength                                                                         420  350  380  370  370  350  250                                  (kg/cm.sup.2)                                                                 Elongation (%)                                                                           300  280  270  200  250  210  150                                  __________________________________________________________________________     (Note)                                                                        Processability was evaluated in terms of the surface condition of the         strand obtained after 15 hours of continuous extrusion and the thermal        coloration of the pellets. The surface condition of the strand follows a      course toward roughening and the thermal coloration of pellets progresses     in the order of light yellow (normal) to yellow to brown.                

Quality was assessed in terms of the degree of entry of grains (degradedresin gels, burnt resin grains, charred resin grains, and unfused gels)sized 1 mm or larger per 30 cm×30 cm of the film prepared from thepellets obtained after 15 hours of operation (≦5 good, 6-20, some, >20abundant) and the tensile strength and elongation (as measured at apulling speed of 500 mm/min, a chuck-to-chuck distance of 50 mm and areference line-to-line distance of 20 mm) of the film.

INDUSTRIAL APPLICABILITY

Shaped products obtainable from the biodegradable composition of theinvention find application in a variety of fields such as packagingmaterials (film, sheet, bottle, cup, tray, can carrier, agriculturalmaterials (agricultural film, bundling tape, etc.) and civil materials(diaper backing sheet, shopping bag, garbage bag, etc.).

It is claimed:
 1. A biodegradable resin composition comprising asaponified ethylene-vinyl acetate copolymer having an ethylenevinylacetate copolymer having an ethylene content of 20 to 60 mole a vinylacetate saponification degree of not less than 90 mole a melt flow indexof 1 to 100 g/10 min as measured under a load of 2160 g at 210° C., anda melt viscosity ratio of ηη₆₀ /η₅ of 0.8 to 2.5 where η₆₀ means themelt viscosity after 60 minutes of standing at 250° C. and the η₅ meansthe melt viscosity after 5 minutes of standing at 250° C. and astarch-based macromolecular substance,wherein said saponifiedethylene-vinyl acetate copolymer and said starch-based macromolecularsubstance occur in a ratio of 80:20 through 20:80 and wherein one ofsaid saponified ethylene-vinyl acetate copolymer and said starch-basedmacromolecular substance is fed to an extruder via its main feeder andmelted in the extruder and the other is fed in a molten state to theextruder via a side feeder, and said saponified ethylene-vinyl acetatecopolymer and said starch-based macromolecular substance are blendedtogether in a molten state in the extruder.
 2. The biodegradable resincomposition of claim 1 wherein the saponified ethylene-vinyl acetatecopolymer is a hydrous saponified ethylene-vinyl acetate copolymerhaving a water content of 20 to 60 weight %.
 3. The biodegradable resincomposition of claim 1 which contains a plasticizer in addition to saidsaponified ethylene-vinyl acetate copolymer and starch-basedmacromolecular substance.
 4. The biodegradable resin composition ofclaim 1 wherein the plasticizer is a polyhydric alcohol containing 2 to4 hydroxyl groups and having a melting point of not lower than 40° C.and a molecular weight of not more than
 600. 5. A laminate comprising alayer composed of a biodegradable resin composition comprising asaponified ethylenevinyl acetate copolymer having an ethylene content of20 to 60 mole % a vinyl acetate saponification degree of not less than90 mole %, a melt flow index of 1 to 100 g/10 min as measured under aload of 2160 g at 210° C., and a melt viscosity ratio η₆₀ /η₅ of 0.8 to2.50 where η₆₀ means the melt viscosity after 60 minutes of standing at250° C. and η₅ means the melt viscosity after 5 minutes of standing at250° C. and a starch-based macromolecular substance,wherein saidsaponified ethylene-vinyl acetate copolymer and said starch-basedmacromolecular substance occur in a ratio of 80:20 through 20:80 andwherein one of said saponified ethylene-vinyl acetate copolymer and saidstarch-based macromolecular substance is fed to an extruder via its mainfeeder and melted in the extruder and the other is fed in a molten stateto the extruder via a side feeder, and said saponified ethylene-vinylacetate copolymer and said starch-based macromolecular substance areblended together in a molten state in the extruder and a layer ofsubstrate material selected from the group consisting of a thermoplasticresin, paper, woven cloth, nonwoven cloth, metal, foil and wood board.6. The laminate of claim wherein said substrate material is a layer ofat least one photodegradable polymer selected from the group consistingof ethylene-CO copolymer, ethylene-vinyl ketone copolymer, polybutadieneand isoprene rubber or a polyolefinic photodegradable polymer containingat least one of said polymers as blended.